I had to look up steps, having no idea what they equate to. Seems to be about 5 miles or 500 kCal, which is quite respectable, but depends on other stuff too like your weight. Also depends how energetic you are doing it. Providing you are up to it, it should be at a pace which makes you sufficiently breathless to interfere with your speech, but to still be able to speak.
If you've been doing this a while and it isn't getting easier/better, I would ask for a blood test including standard blood counts and vitamin B12 level. (Don't take vitamin B12 except under regular monitoring of your GP, to make sure you are only taking it if below normal.)
Exercise is the antidote to fatigue.